1. Field of the Invention
The present invention relates to a polarized light illumination apparatus for uniformly illuminating a rectangular illumination area with light polarized in the same direction, and also to a projector using such a polarized light illumination apparatus. More particularly, the present invention relates to a structure for combining lights emitted from two light sources such that the resultant combined light is polarized in the same direction.
2. Description of Related Art
In liquid crystal display devices using a modulating element such as a liquid crystal element which modulates light polarized in a particular direction, only one component of two types of polarized light components included in light emitted from a light source is used. To obtain a projected image with high brightness, it is required to increase the utilization efficiency of light. However, when a projector is constructed using a single light source, the utilization efficiency of light has a practical upper limit. Thus, one technique of projecting a high-brightness image is to increase the amount of light by using a plurality of light sources.
However, if a plurality of light sources are arranged in a simple fashion, the overall area of the light source image becomes greater by a factor corresponding to the number of light sources. As a result, the angle of light (illumination angle) striking an illumination area also increases by a corresponding factor. This means that the amount of light per unit area is the same as that obtained with a single light source. In other words, the amount of light per unit area cannot be increased by using a plurality of light sources arranged in the above-described fashion.
Even when the amount of light can be increased by using a plurality of light sources, if only one component of two polarized light components of light emitted from the light sources is used, one-half of the total amount of light is wasted, which reduces its effectiveness by half.
It is an object of the present invention to provide a polarized light illumination apparatus including a plurality of light sources and capable of emitting light using both polarized light components without causing an increase in the illumination angle. It is another object of the present invention to provide a projector capable of forming a projected image with extremely high brightness.
To solve the issues described above, the present invention provides a polarized light illumination apparatus comprising:
first and second light sources;
a polarized light separating and combining optical element including: a first polarization separating film which transmits a linearly polarized light contained in light emitted from the first light source and polarized in a direction parallel to an incidence plane but which reflects a linearly polarized light contained in the light emitted from the first light source and polarized in a direction perpendicular to the incidence plane; and a second polarization light separating film which transmits a linearly polarized light contained in light emitted from the second light source and polarized in a direction parallel to the incidence plane but which reflects a linearly polarized light contained in light emitted from the second light source polarized in a direction perpendicular to the incidence plane;
a first condensing and reflecting optical element including a plurality of small condensing and reflecting elements for substantially reversing the traveling direction of the linearly polarized light transmitted through the first polarization separating film and forming a condensed light image;
a second condensing and reflecting optical element including a plurality of small condensing and reflecting elements for substantially reversing the traveling direction of the light reflected by the first polarization separating film and the second polarization separating film and forming a condensed light image;
a third condensing and reflecting optical element including a plurality of small condensing and reflecting elements for substantially reversing the traveling direction of the linearly polarized light transmitted through the second polarization separating film and forming a condensed light image;
a first polarization-state conversion optical element disposed between the polarized light separating and combining optical element and the first condensing and reflecting optical element;
a second polarization-state conversion optical element disposed between the polarized light separating and combining optical element and the second condensing and reflecting optical element;
a third polarization-state conversion optical element disposed between the polarized light separating and combining optical element and the third condensing and reflecting optical element; and
a polarization conversion optical element for aligning the direction of polarization of the linearly polarized lights combined by the polarized light separating and combining optical element; the polarized light illumination apparatus being characterized in that a center axis of the light which is incident on the polarization conversion optical element after being reflected by the small condensing and reflecting elements of the first and third condensing and reflecting optical elements and a center axis of the light which is incident on the polarization conversion optical element after being reflected by the small condensing and reflecting elements of the second condensing and reflecting optical element are parallel to each other and do not overlap each other.
The construction of the polarized light illumination apparatus according to the present invention is described in further detail below.
Of the components of the light polarized in random directions (hereinafter, referred to as the randomly polarized light) emitted from the first light source, a linearly polarized light component polarized in a direction parallel to the incidence plane passes through the first polarization separating film, whereas a linearly polarized light component polarized in a direction perpendicular to the incidence plane is reflected by the first polarization separating film. On the other hand, of the components of the randomly polarized light emitted from the second light source, a linearly polarized light component polarized in a direction parallel to the incidence plane passes through the second polarization separating film, whereas a linearly polarized light component polarized in a direction perpendicular to the incidence plane is reflected by the second polarization separating film. Herein, the xe2x80x9cincidence planexe2x80x9d is a technical term used in the art of optics to represent a virtual plane including the center axis of a light incident on a film, and also including the normal to the film.
The linearly polarized light which has passed through the first polarization separating film passes through the first polarization-state conversion optical element and is then reflected by the first condensing and reflecting optical element back to the first polarization-state conversion optical element. The light again passes through the first polarization-state conversion optical element and travels toward the polarized light separating and combining optical element. In the above process, the light is divided by the first condensing and reflecting optical element into a plurality of intermediate lights and converted to linearly polarized lights with a polarization rotated by about 90xc2x0 when the light passes twice through the first polarization-state conversion optical element. Thus, when the light returns to the polarized light separating and combining optical element, the light is reflected by the first polarization separating film and directed toward the polarization conversion optical element. Herein, the polarized light directed toward the polarization conversion optical element is referred to as first polarized light.
The linearly polarized light reflected by the first polarization separating film and the second polarization film passes through the second polarization-state conversion optical element, and is then reflected by the second condensing and reflecting optical element. After that, the light again passes through the second polarization-state conversion optical element and travels toward the polarized light separating and combining optical element. In the above process, the light is divided by the second condensing and reflecting optical element into a plurality of intermediate lights and converted to linearly polarized lights with a polarization rotated by about 90xc2x0 when the light passes twice through the second polarization-state conversion optical element. Thus, when the light returns to the polarized light separating and combining optical element, the light passes through the first and second polarization separating films and travels toward the polarization conversion optical element. This polarized light directed toward the polarization conversion optical element is a light polarized in a direction substantially perpendicular to the polarization direction of the first polarized light. This polarized light is herein referred to as second polarized light.
The linearly polarized light which has passed through the second polarization separating film further passes through the third polarization-state conversion optical element and is then reflected by the third condensing and reflecting optical element. The light again passes through the third polarization-state conversion optical element and travels toward the polarized light separating and combining optical element. In the above process, the light is divided by the third condensing and reflecting optical element into a plurality of intermediate lights and converted to linearly polarized lights with a polarization rotated by about 90xc2x0 when the light passes twice through the third polarization-state conversion optical element. Thus, when the light returns to the polarized light separating and combining optical element, the light is reflected by the second polarization separating film and directed toward the polarization conversion optical element. This light is polarized in the same direction as the first polarized light. Thus, this light is also referred to as the first polarized light.
The center axes of the first and second polarized lights are parallel to each other, and they do not overlap each other. As a result, the condensed light image of the first polarized light and the condensed light image of the second polarized light are formed at locations different from each other. This makes it possible for the polarization conversion optical element to align the polarization direction of the first polarized light and the polarization direction of the second polarized light in the same direction.
Therefore, even though two light sources are used in the polarized light illumination apparatus according to the present invention, the lights emitted from the two light sources can strike the same area as that illuminated with light emitted from a single light source without causing an increase in the incident angle (illumination angle) of the illumination light to the illumination area. This means that the amount of light per unit area can be increased to a level approximately two times greater than that obtained with a single light source. This makes it possible to illuminate the illumination area very brightly. By superimposing intermediate lights separated by the respective condensing and reflective optical elements into a single light striking a single location in the illumination area, it becomes possible to uniformly illuminate the illumination area. Therefore, if the polarized light illumination apparatus according to the present invention is used as a light source of a display device, an image with excellent uniformity can be obtained. Furthermore, in the polarized light illumination apparatus according to the present invention, the randomly polarized lights emitted from the first and second light sources can be combined into a single type of polarized light without causing substantially any loss. Therefore, if the polarized light illumination apparatus is employed in a display device including a modulator such as a liquid crystal device for modulating a light polarized in a particular direction, a very bright image can be obtained.
Furthermore, as described above, the center axis of the light which is incident on the polarization conversion optical element after being reflected by the small condensing and reflecting elements of the first and third condensing and reflecting optical elements and the center axis of the light which is incident on the polarization conversion optical element after being reflected by the small condensing and reflecting elements of the second condensing and reflecting optical element are parallel to each other. This means that lights reflected by the small condensing and reflecting elements of the first to third condensing and reflecting optical elements are incident at substantially the same angle upon the polarized light separating and combining element. Therefore, even when the polarized light separating and combining characteristics of the polarized light separating and combining element is sensitive to the incident angle of light, polarized light separation and combination can be accomplished in a highly reliable fashion, and thus a uniform illumination light can be obtained.
Although the first to third condensing and reflecting optical elements are not limited to specific locations, it is required that they be disposed such that the first and third intermediate lights overlap each other on the polarization conversion optical element and such that the first and third intermediate lights do not overlap the second intermediate lights on the polarization conversion optical element.
In the present invention, the shape of the opening of each small condensing and reflecting element may be similar to the shape of an area to be illuminated. The lights emitted from the light sources are divided by the condensing and reflecting optical elements into a plurality of lights and, eventually, superimposed upon one another in the illumination area. Thus, it becomes possible to direct the lights emitted from the light sources to the illumination area without producing a loss.
In the present invention, a condensing optical element including a plurality of condensing elements for condensing the light emerging from the polarized light separating and combining element may be disposed on the incident side or the emitting side of the polarization conversion optical element so that a plurality of lights produced by means of dividing performed by the condensing and reflecting optical elements are condensed and directed to particular locations of the polarization conversion optical element, thereby achieving a high efficiency in polarization conversion performed by the polarization conversion optical element. In the case where the number of small condensing and reflecting elements is different among the first to third condensing and reflecting optical elements, the number of small condensing elements of the condensing optical element may be set to be twice the number of small condensing and reflecting elements of the condensing and reflecting optical element having the greatest number of small condensing and reflecting elements.
In the present invention, a superimposing optical element for superimposing the lights emerging from the polarization conversion optical element upon one another in the illumination area may be disposed on the emitting side of the polarization conversion optical element. The superimposing optical element allows the plurality of lights produced by the condensing and reflecting optical elements via the dividing process to reach the illumination area in an effective fashion, thereby allowing an improvement in the illumination efficiency.
In the present invention, an optical path changing element for changing the optical path of the light emerging from the polarization conversion optical element may be disposed on the emitting side of the polarization conversion optical element. If the optical path changing element is disposed such that the resultant illumination light is directed in a direction parallel to a plane defined by the optical axes of the two light sources having rather large sizes, then it becomes possible to reduce the size of the polarized light illumination apparatus in one direction. That is, a polarized light illumination apparatus with a small thickness can be realized. If this polarized light illumination apparatus is employed as a light source of a projector, it is possible to realize a projector with a small size.
In the present invention, the small condensing and reflecting elements of the first to third condensing and reflecting optical elements each may include a plurality of curved surface reflecting mirrors. Alternatively, the small condensing and reflecting elements of the first to third condensing and reflecting optical elements may be formed of a lens and a reflecting surface formed on the side of the lens opposite to the polarized light separating and combining element so that the lights emitted from the light sources are easily separated into a plurality of intermediate lights. If the curved surface reflecting mirrors are constructed in a decentered fashion or the lenses are constructed in a decentered fashion, it becomes possible to effectively direct the lights to the illumination area without using the superimposing optical element, and it also becomes possible to reduce the size of the polarization conversion optical element and the condensing optical element.
The polarized light illumination apparatus according to the present invention may be employed in a projector including: an optical modulator for modulating light emitted from the polarized light illumination apparatus; and a projecting optical system for projecting the light modulated by the optical modulator.
The polarized light illumination apparatus may also be employed in a projector capable of displaying a color image, wherein the projector includes: a colored-light separating optical element for separating light emitted from the polarized light illumination apparatus into a plurality of colored lights; a plurality of optical modulators for modulating the respective colored lights separated by the colored-light separating optical element; a colored-light combining optical element for combining the lights modulated by the plurality of optical modulators; and a projecting optical system for projecting the light combined by the colored-light combining optical element.
The polarized light illumination apparatus may also be employed in a projector including: a reflective optical modulator for modulating light emitted from the polarized light illumination apparatus; a polarized light separating optical element for separating a plurality of polarized light components contained in the light emitted from the polarized light illumination apparatus and in the light modulated by the reflective optical modulator, from one another; and a projecting optical system for projecting the light modulated by the reflective optical modulator and then emitted via the polarized light separating optical element.
The polarized light illumination apparatus may also be employed in a projector including: a colored-light separating optical element for separating light emitted from the polarized light illumination apparatus into a plurality of colored lights; a plurality of reflective optical modulators for modulating the respective colored lights separated by the colored-light separating optical element; a plurality of polarized light separating optical elements for separating a plurality of polarized light components contained in the colored lights separated by the colored-light separating optical element and in the colored lights modulated by the plurality of reflective optical modulators, from one another; a colored-light combining optical element for combining the lights modulated by the plurality of reflective optical modulators and then emitted via the plurality of polarized light separating optical element; and an optical projection system for projecting the light combined by the colored-light combining optical element.
As described above, if the polarized light illumination apparatus according to the present invention is employed, it is possible to realize a projector capable of forming a projected image with a high and uniform brightness. Because the polarized light illumination apparatus according to the present invention emits light with the polarization aligned in the same direction, it is particularly suitable for use in protector using a liquid crystal device as an optical modulator.
In the projector described above, it is desirable that at least one of the first and second light sources be constructed to be detachable. This allows a user to easily carry the projector by detaching one of the light sources.
Furthermore, in the projector described above, it is desirable that at least one of the first and second light sources be capable of selectively turning on. This allows only one of the light sources to be selectively turned on, for example, when the projector is driven by battery, thereby making it possible to increase the battery life. That is, it is possible to select the brightness of the projected image by turning on only one of the two light sources or both light sources, depending on the brightness in the environment or preferences of a user. More specifically, when the projector is used in a light environment, both light sources may be turned on, whereas only one of the light sources may be turned on when it is used in a dark environment.
Furthermore, in the projector described above, the first and second light sources may be different in the spectral characteristics or brightness characteristics of emitted light. This makes it possible to easily adjust the color tone of the illumination light as desired.